Watershed Module overview

Algoritm Steps (Directional)

1. Init: Predefined water terrains that intersect input watershed areas are marked with a unique id, starting from 1. The values of these cells are considered minima and are never adjusted by the algoritm described below.

1. Step 1 (applied once): Convert Input data to cell references, in 8 directions. Cells without a direction angle become a plateau with a unique id.
2. Step 2 (loop until stable): Calls without a reference to other are re-evaluated. Such a cell will reference the first neighboring cell that flow away from it.
3. Step 2B (only once): Neighboring cells that reference each other, are both set back to being a plateau. They can now be seen as a minima.
4. Step 3A (only once): For cells that are marked as a plateau, mark them now as minima with a unique id.
5. Step 3B (loop until stable): Union minima cells ids, by giving them both the lowest ids of the two.

Tips

• When using a Water Overlay's Flow direction result as an input for the Watershed Overlay, it is important to consider what rain settings are used. Generally, you want select a rainfall big enough for local minima, due to small depressions in the terrain, to disappear. On the other side, the rainfall should not be too big for the marked ditches it should end up in.